Hi Brian:
Great! sorry i missed that one. Would it be useful to add the mathematics or a reference to such in Appendix F?
Brian Eaton wrote:
> Hi John,
>
> CF sec 5.6 has an example of how to represent the rotated pole grid.
>
> The "axis" attribute is not well defined for any use other than it's
> original one which is that it provides an easy way to identify
> lat,lon,lev,time axes without having to parse the "units" attribute.
> It has always been only an optional attribute in CF. It was included for
> backwards compatibility with the GDT convention which was one of the
> precursors to CF.
>
> Brian
>
>
>
> On Mon, Nov 13, 2006 at 12:37:59PM -0700, John Caron wrote:
>
>>
>>Brian Eaton wrote:
>>
>>>Hi Jonathan,
>>>
>>>Here is the note that resulted in the wording of CF sec 4.1:
>>>
>>>On Wed, 12 Dec 2001, Jonathan Gregory wrote:
>>>
>>>
>>>>Returning to the use of latitude and longitude for things which aren't
>>>>really.
>>>>I am happy with what we decided, but another possible pitfall has
>>>>occurred to
>>>>me. In the case of a rotated pole, it would be very natural for a
>>>>data-writer
>>>>to use standard-looking lat and lon axes for the *rotated* lat and lon.
>>>>If we
>>>>don't want this, we ought to specifically forbid it, I would suggest, by
>>>>adding notes in 4.1 and 4.2 e.g.
>>>>
>>>>Coordinates of latitude with respect to a rotated pole should be given
>>>>units
>>>>of "degrees", not "degrees_north" or equivalents, because applications
>>>>which
>>>>use the units to identify axes would have no means of distinguishing such
>>>>an
>>>>axis from real latitude, and might draw incorrect coastlines, for
>>>>instance.
>>>>It would also not generally be appropriate to attach an axis attribute to
>>>>a
>>>>rotated-latitude coordinate variable. Such a variable can be identified by
>>>>a standard_name of "grid_latitude".
>>>
>>>
>>>I believe that the reason for excluding the use of "axis" is that the
>>>default interpretation of axis="X" is to identify the longitude axis.
>>>Allowing axis="X" to denote either the rotated latitude or longitude axes
>>>is a recipe for confusion and unlikely to be helpful to any application.
>>
>>Hmm, I was thinking the main reason to identify axis=X was for projection
>>coordinates, which these can be seen as analogous to. But now I realize
>>that we look for the standard name "projection_x_coordinate", so maybe
>>thats wrong.
>>
>>Still, the question remains how to represent rotated lat/lon in CF?
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Received on Mon Nov 13 2006 - 14:17:30 GMT
